Please see the Spellbreak installation instructions article for more information.
Anyone who purchased a Founder Pack after November 5, 2018 will only need to log-in to the launcher and their key will automatically be in the system—you will not need to redeem anything. The key you received via email is for your records and it will work through all phases of the development of Spellbreak for various things, but we may need to issue new keys to you occasionally.
If you bought your pack before November 5, 2018 and you are attempting to use your key in Steam (and you already had the pre-alpha), it may tell you that the product you have is already owned. That is fine for this stage of testing, but hold onto that key for later (do not give this key away; it is not the same as the pre-alpha keys, which will expire).